By TODD BISHOP, P-I REPORTER

Published 10:00 pm, Sunday, August 24, 2008

THE ADVENT OF municipal Wi-Fi systems, blanketing some cities with wireless Internet access, brings one thought to the mind of the modern computer geek.

"Hey, why not use it while I'm driving around?"

Of course, for the person behind the wheel, there's a big reason why not. But computer systems and passengers in moving cars, shuttles and other vehicles might benefit from connecting to community Wi-Fi networks on the move.

That's the basic idea behind recent work by researchers at the University of Massachusetts, Microsoft and the University of Washington. Although many people already use cellular broadband networks for mobile Internet connections, community Wi-Fi systems offer technical advantages and a lower cost of access.

But for all the potential benefits, the researchers discovered a big challenge: Hiccups can occur in the Wi-Fi signal as a vehicle moves through the wireless network. The problem is particularly evident during what's known as a "hard handoff" -- moving from the range of one wireless base station to another.

The researchers came up with a solution that lets computers and devices take advantage of multiple base stations at once to smooth the transition.

Based largely on a test deployment on the Microsoft campus, the researchers say the technique makes it noticeably easier to use interactive software applications, make Internet voice calls and do other things that require a steady connection.

"Today's Wi-Fi handoff protocols are incredibly fragile in outdoor environments and mobile environments," Ratul Mahajan, a Microsoft researcher working on the project, said in an interview. Under existing approaches, he explained, computers and devices are "artificially limited to talking to only one access point, or only one base station at a time, even though there may be other base stations" in the area.

When it comes to moving vehicles, that results in unpredictable periods in which the connectivity drops sharply. Even if it's for a short time, the loss of reception can cause problems for some types of software programs.

For example, a passenger making an Internet phone call on a moving bus, using a city's Wi-Fi system, could lose the call entirely during the transition.

The solution devised by the researchers takes advantage of the fact that Wi-Fi is a broadcast medium. It's possible for multiple base stations to receive the blocks of data, or packets, transmitted wirelessly from computers and devices on the system.

Under their system, dubbed Vi-Fi, a device or computer in a moving vehicle selects one base station at a time as an "anchor," or primary reception point. But it also lets other base stations in the system act as auxiliaries at any given moment.

The technological trick is a high-tech algorithm in the system that uses probabilistic reasoning to figure out the chance that a packet received by an auxiliary base station wasn't received by the anchor. Depending on what it determines, the auxiliary base station can relay the packet to the anchor base station as a backup.

The approach works in the other direction as well -- letting the auxiliary base station relay a packet to a vehicle if the algorithm determines that the packet sent by the primary base station wasn't received by the computer or device.

The Microsoft, UW and Massachusetts researchers acknowledge they aren't the first to suggest connecting to Wi-Fi networks from vehicles. However, they believe their approach is unique.

For the record, Microsoft's Mahajan doesn't want the research to lead to systems that encourage drivers to be distracted by Web browsing. But he sees many practical applications, such as the ability for in-car satellite navigation systems to access the Internet and automatically download maps while passing through a Wi-Fi zone.

Next up: The researchers have been talking with Microsoft's internal IT department about a broader test deployment of the technology on the campus.